Recovery of hydrogen fluoride catalyst



' fluoride, and the cke.

Patented Apr. 29, 1947 RECOVERY F HYDROGEN FLUORIDE CATALYST James D.Gibson, Bartlesville, Okla.,.assignor to Phillips Petroleum Company, acorporation of Delaware Application August 23., 1943, Serial N0. 499,705

6 Claims.

1 This invention relates to the regeneration of deuorination agents orcatalysts. In a more Aparticular embodiment it relates to theregeneration of contact material spent in removing organically combinedfluorine from hydrocarbon materials obtained in processes utilizingiluorine compounds. In another embodiment it relates to the recovery ofluorine, as hydroiiuoric acid, from the defluorination agent.

In the manufacture of hydrocarbons, or hydrocarbon fractions, byprocesses in which fluorine-containing catalysts are used, smallproportions of organic uorine-containing by-products are formed. Theseprocesses may involve various reactions, among which are polymerization,isomerization and alkylation of relatively lowboiling hydrocarbons toproduce motor-fuel hydrocarbons, that are eliected in the presence ofcatalysts comprising one or more of such liucrine compounds ashydrofluoric acid, boron tri..

Although the exact nature or composition of these organicuorinecontaining by-products has not been definitely established, theyare believed to be predominantly alkyl and/or aryl uorides. They are notcompletely removed by washing the hydrocarbon fractions with alkalinesolutions. They tend to decompose at elevated temperatures, such asthose employed in fractional distillation of the hydrocarbons,thereby'forming hydrouoric acid, which is corrosive, especially in thepresence of moisture. In gaseous hydrocarbon fractions they may thuscause corrosion of handling equipment; in liquid, and especiallymotor-fuel, hydrocarbon fractions, they are obviously undesirable forsimilar reasons.

The uorine in these by-products may be removed from hydrocarbonmaterials by contactking at an elevated temperature betweenapproximately 100 F. and approximately 600 F. With one or more solidporous deuorination agents, such as granular metal oxide contactmaterials having catalytic hydrogenation and/or dehydrogenationproperties, as is disclosed and claimed in Frey 2,347,945, filed June16, 1941, issued May 2, 1944. Among suitable materials are alumina gel,Activated Alumina, dehydrated bauxite, chromium oxide, and mixtures ofalumina and chromium oxide, zirconia, .calcium oxide, magnesium oxide,etc. Although deiiuorination by these materials is highly effective, theuorine thus removed represents an undesirable consumption of theoriginal duerme-containing catalyst; consequently, the recovery of thisiluorine in a useful form is desirable. the useful life of adeuorination agent is limited, regeneration of the deiluorination agentis also desirable. y

An object of this invention is to Vregenerate spent porouscontact'materials used for the re- Furthermore, since moval of organicuorine from hydrocarbon materials.

Another object of this invention is to recover iluorine as substantiallyanhydrous hydroiluoric acid from a porous contact material used todeuorinate a hydrocarbon material.

A further object of this invention is to regenerate deuorination agents.

Another object of this invention is to regenerate .bauxite used as adefluorinating agent.

Other objects and advantages will be apparent from the accompanyingdescription and discussion.

In accordance with this invention, a spent porous defluorination agentis regenerated by treatment with superheated steam, whereby the fluorineis removed as hydrouoric acid, which may be concentrated to theanhydrous condition.

An understanding of the invention may befacilitated by reference to theaccompanying drawing, which in a schematic flow-diagram shows a mode ofpracticing the invention. For the sake of concreteness, thisflow-diagram shows a mode of practicing the invention in connection witha hydrofluoric acid alkylation system..

A hydrocarbon feed enters the system through one or more inletsrepresented by inlet 6 controlled by valve 'l and'is passed to alkylatorl0.

. This feed comprises: an alkylatable hydrocarvco bon, usually anisoparafn, such as isobutane; an alkylating agent, usually an oleiin,such as one or more of the butenes; and usually some incidentallypresent diluents, such as normal butane and propane. The exactcomposition of the feed may vary within broad limits; a generallysatisfactory mol ratio 0f alkylatable hydrocarbon to alkylating agent inthe feed is from 4:1 to 10:1, although a mol ratio as high as :1 may bemaintained if desired. Conoentrated hydrofluoric acid enters the systemthrough inlet 8 controlled by valve 9 and is passed to alkylator lll, inWhich the acid and the hydrocarbon feed are intimately mixed by anysuitable agitation device. Operating conditions in alkylator l0, as forexample for alkylating isobutane with butylenes, are a temperature of 30to 150 F., a pressure suiiicient to maintain al1 components in liquidphase, a contact time or time of residence in the alkylator of about 1to 30 or more minutes, and a volume ratio 0f acid to hydrocarbon from2:1 `to 1:2; however, conditions outside of these ranges may beused.

The effluent mixture from alkylator ll) is passed through conduit llcontrolled by valve I2 to settler 20, in which the mixture is separated,as by gravity and/o1' centrifugation, aided, if desired, by cooling,into a lighter or hydrocarbon phase and a heavier or acid phase. Thehydrouoric acid phase may be recycled through con-A duit 2l controlledby valve 22 to alkylator l0:

usually.hoyvever, Va part of .this Vphaseis withdrawnfas throughpoutlet23 contrclledfby valve 24, for purication, by means not shown, beforebeing returned to alkylator it. The hydrocarbon phase is passed throughconduit 25 controlled'by valve 26 to azeotrope column jilin which iteisseparated by fractional distillation into two fractions.

The overhead fraction from ,azeotrope column 3B is a low-boiling orazeotropic mixture of hydrofluoric acid and low-boiling parafnhydrocarbons such as propane and isobutane. This fraction is passedthrough conduit 3l controlledby valve 32 to condenser 33. The liquideiiiuent from condenser 33 is passed through conduit .'ll tosettler35,-in which a heavier or hydrofluoric acid phase is separatedfrom a lighter or hydrocarbon phase. The hydrocarbon phase is returnedas --reilux to -azetrope-column 39 through conduit 3c controlledk bylvalve 3l, and the acid phase. is recycled through conduit-38 controlled'by valve' 39 toalkylator l0.

The kettle fractionfrom azeotrope vcolumn Si), which is substantiallyfree from hydroluoric acid ,but contains a small proportion of.organically combinedfluorine, ispassed through conduit l controlledby-valve 5'! to defluorinator 6c. In deuorinator et it is contacted witha solid porous metal oxide contact material capableof removingorganically combined fluorine from hydrocarbons, such gas. alumina-gel,Activated Alumina, dehyhdrated: bauxite, chromium oxide, or a. mixtureof alumina and chromium. oxide, etc., as .previously discussed.Althoughthe exact mechanism. of the removalof organically combinednuorine is not fully understood, it maybe at least partially rep-`resented by the Vfollowing reaction scheme:

tn/here'R.-and Rvare alkyl radicals or hydrogen` andsM;` is a trivalentmetal.

For. the sake of concretenessof illustration, the .contactmaterial maybe consideredto bedehydrated-ba-uxite, which is preferred because ofVits general availability at low cost. The-hydrocar- .bonrnaterial Amaybein either the liquid or the l gaseousv state; as thematerials involvedin this process are easily maintained-in theliquid phase under the,preferred operating conditions, liquidlhase treatmentl is preferable.Asuitabletem- A:1oerature for defluorination is usually in the-range.offapproximately 150 to 350 F. A generally suit- -;ab1e. space-Velocityis l to 2 liquid volume-s per hour, althoughthe optimum space velocityde- ...pends upon the specific contact material used, the-temperature,qthe--iluorine content of the material .to be-treated,and-the degree of defluorination desired. lI-heoptimum combination ofdeuoringationrconditions for any specific-case may be exgperimentallydetermined by anyone skilled in the-art.

The -ieflluent from .deiluorinator ,Ell is 4passed nthroughconduitlcontrolled by vali/c62 to frac- .-.tionatingrmeans lil, .whichusually comprises a 4.system of two or .more fractionating columns. Inthis means,A the .hydrocarbonmaterial is sepa- .ratediintosome or allofthe following fractions:

t1) .arminor fraction comprising chieflysubstantiallyffluorine-freeprQpane, Vwhich is Withdrawn .from .thesystem through outlet 1 l controlledy by valve 12; (2) a major fractioncomprisingY prinwhich. is recycled through. conduitf'l controlled byvalveltl to alkylator I0; (3) a fraction com-l prising mainlysubstantially fluorine-free normal Atrolled by valve Z.

butane which is Withdrawn from the system, .through outlet 'I5controlled by valve 16; and

(4) a fraction boiling above butane, Which ordinarily is ,passed throughconduit 83 controlled by valveltorerun column 90, but which may bepassedthrough conduit ll controlled by valve i8 to defluorinator 80 forremoval of any residual objectionable proportion of organic uorineunder` conditions similar to those described for defluorinator 6B,except that the temperature may have to be somewhat higher, and thenthrough -conduit Si controlled by valve 2'to conduit 83 and rerun column9G.

lFrom rerun` column 98 a'mixture of hydrocarbons boiling inthemotor-fuel range is removed las an overhead fraction through outlet 9!con- A -small relatively high-boiling fraction of hydrocarbons boilingabove the motor-fuel range is withdrawn from vcolumn through outlet 93controlled by valve S4.

The present invention is primarily concerned with regeneration of thedeluorination agent or contact-material and with recovery as hydrouoricacid of the absorbed fluorine. When the contact material indefluorinator 6B has become spent to such a degree that regeneration isconsidered desirable, as, for example, when the bauxite contains 30 to40 per cent of `its own Weight of iluorine, the hydrocarbon stream fromazeotrope column Bills diverted through defluorinator 5B by opening ofvalves 52 and .in conduits 53 and 55, respectively, and closing'ofvalves 5l`and 62 in conduits 5I and'l, respectively. Defluorinator issimilar in construction, content, and operation to defluorinator 60,although a different contact material .may be used if desired. Forregeneration of the defluorination agent, steam enters the systemthrough inlet loi controlled by valve |02. It is passedthrough'superheater lil, which is any suitable apparatus for rai-singthe temperature of the steam to the generally satisfactory temperaturerange of .approximately 660 to 10`00 F., preferably3'850 to 950 F.Thesuperheated steam is passed through conduit H35 controlled by valveii to dei'luorinator Si), Where it is passed through the spent bauxiteat a rate equivalent to 0.1 to 5 liquid volumes .of waterper volume ofdeiluorina- "tion agentper hour, depending on the specificoontactmaterial, the temperature, .theuorine content of the contactmaterial, and the desired degree o regeneration. The optimum operatingconditions `.for any specific .application of the invention .may beexperimentally determined by anyoneskilled in the art, in the lightofthe di-sclosure and discussion presented herein.

The regeneration eiiuent from deuorinator 63 is passedthroughconduit |09and valve MBA. If desiredlit .may be vvithdravvn through outlet H5controlled. by valve I I6, but it is preferably passed to hydroliuoricacid recovery means |20 through conduit |09. controlled by valve i l0. YHydrofluoric acid recovery means 2t may comprise any sys- .tem ofapparatus suitable for recovering substantially anhydrous hydrofiuoricacid from mixtures with Water. The recovery may .be effected in variousways, .as by multiple fractional distillation at different pressures,electrolysis, .or the `like,.b.ut it .is usually preferably effected.through formation of ,a complex or compound with an agent of the typeof high-boiling others, nitrogen bases, metal salts that form acidfluorides, etc., removing the acid-depletedwater, and reliberating thehydrofluoric acid in substantially anhydrous form, preferably by heat. Apresently preferred method of operation is to contact the vaporousmixture of steam and hydrogen iuoride with a metal fluoride that iscapable of forming a complex acid salt with hydrogen fluoride,especially the liiuorides of the alkali and the alkali earth metals.There is also some indication that other iluorides, such as aluminumfluoride, will also form such complex salts. These metal uorides arepreferably used as a large mass of granular salt. Although they may beused alone, it is often preferable to have them deposited upon a poroussupporting material such as charcoal, bauxite, alumina gel and the like,preferably of a non-siliceous character. This contacting should becarried out under temperature and pressure conditions such that a liquidaqueous phase is not present and such that the partial pressure of thehydrogen fluoride is substantially greater in the vapor mixture than isthe partial pressure of hydrogen fluoride in the complex salts beingformed. It is preferred, however, that the temperatures not exceed about350 to 400 F.; when working at a pressure at about atmospheric atemperature of labout 24.43 F. has been found quite satisfactory. Whenthe mass of metal salt is suiiiciently saturated with hydrogen fluorideso that efficient removal of hydrogen fluoride from the vaporous mixtureis no longer vobtained another mass of metal iiuoride may be put intooperation and hydrogen iluoride recovered in a concentrated or anhydrousform from the saturated mass. This may be eiected simply by heating themass under `a reduced pressure and cooling and condensing the eilluentvapors. In some instances it may be desirable to pass through the massduring this heating an inert gas such as air, nitrogen, or a low-boilinghydrocarbon and I have obtained satisfactory operation by using butaneas such a gas. Substantially acid-free steam or Water is withdrawnthrough outlet H3 controlled by valve H4, and substantially anhy- -zdrous hydroiiuoric acid is recycled to alkylator I through conduit I ilcontrolled by valve H2.

In a case Where a low-boiling hydrocarbon is passed through recoverymeans |20 for removal and recovery of hydrogen iluoride from the metalfluoride by heating, .the resulting eiiiuent passes out line Ell andthrough Valve ||2 to condenser |2|. From condenser I2|, where theeiiluent is liquefied, a liquid mixture is passed to separator |23 byline |22. In separator |23 the liquid mixture separates into two phases,a liquid hydrocarbon phase and a heavier liquid hydrogen uoride phase.The hydrocarbon phase is withdrawn from separator |23 through line |26,and the liquid hydrogen fluoride phase is Withdrawn through line |24 andrecycled by lines |25 and 2| to the alkylator l0. The liquid hydrocarbonphase which is removed from separator |23 through line |26 is passed toa heater |21. The

hydrocarbon phase is vaporized in heater |21 and recycled to recoverymeans |20 by line |28. Make-up hydrocarbon may be added through line|29, when necessary. 'VThe hydrogen fluoride removed from separator |23by line |24 is substantially free from Water and the hydrocarbon. Toremove hydrogen fluoride dissolved in the liquid hydrocarbon phase or torecover 4the hydrogen uoride when the condensed effluent from heatingzone l2@ contains an amount of hydrogen fluoride below its solubility inthe hydrocarbon comprising the effluent, the liquefied hydrocarbon maybe treated in conventional manner familiar to those skilled in the artfor recovery of the dissolved hydrogen fluoride. One method for recoveryof dissolved hydrogen fluoride in a liquid hydrocarbon is exempliiied bythe present invention in which the dissolved hydrogen fluorideis removedfrom the hydrocarbon phase from settler 20 by distilling the hydrocarbonphase in azeotrope column 30 of the drawing. For more detailedinformation regarding the recovery of disvsolved hydrogen uoride from aliquid hydrocarbon fraction, Patent No. 2,320,629 of Matuszak, issuedJune 1, 1943, may be consulted.

When no inert gas, such as a 10W-boiling hydrocarbon, is passed throughrecovery means |20 the hydrogen fluoride removed therefrom` is passeddirectly through lines lll, condenser |2I, and lines |25 and 2| toalkylator lil without passing through separator |23.

The contact material in deluorinators 50 and Sii is regenerated insimilar manner when it has become spent to such a degree thatregeneration is desirable. In regenerating the material present indeiiuorinator 5U, the hydrocarbon stream from column 30 is diverted andagain passed through defiuorinator 6B, and superheated steam is passedthrough conduit m3 controlled by valve |64. As in the previouslydescribed regeneration of defluorinator 6|?, the regeneration eii'iuentfrom defluorinator 50 is passed through conduit |01 and valve |38. Ifdesired, it may be withdrawn through outlet H5, but preferably is passedto the recovery means |22 through conduit |29.

Many other arrangements of apparatus suitable for practicing theinvention may be devised by anyone skilled in the art Without departingfrom the scope and spirit o the invention.

AnV understanding of some aspects of the invention may be further aidedby the following examples:

Example I The hydrocarbon eluent from the azeotrope column of acontinuous hydrouoric acid alkylation system substantially `as indicatedin the drawing was passed through dehydrated bauxite for the removal oforganically combined fluorine. When the luorine content of the bauxitereached 31.6 Weight per cent, the hydrocarbon stream was stopped.

Superheated steam at different temperatures and space velocities waspassed through a portion of the used bauxite to eiect regeneration. Thefollowing results were obtained:V

Stean1,` equivalent Fluorm Time, Temp liquid volume remove Period o asHF hr. F water per I vol. bauxite cumulatwe per hour per cent 3. 0 5900. 14 1. 8 2. 3 600 0. 61 12. 6 2. 0 605 0. 5' 19. 5 1. 8 600 1. 0 27.6 1. 1 610 0. 9 35. 8 3. 6 600 l. 2 59. 2 2. 6 880 1. 2 87. 2 1. 0 910O. 9 90. 8 1. 9 94() 0. 74 94. 3 2. 3 S80 0. 34 94. 9

Substantially complete removal of iiuorine was effected. The regeneratedbauxite was suitable for further use in defluorination, and the efliuentmixture of steam and hydroiiuoric acid was separable to yieldsubstantially anhydrous hydrouoric acid. s s

Example II Dehydrated bauxite was used for removal of organic fiuorinefrom a hydroiiuoricacid-free paralnic product of a parain conversionprocess. This bauxite, after such use, contained 31.6 Weight per centuorine. It was regenerated by superheated steam with the followingresults:

The regenerated bauxite Was suitable for further use in defluorinationof hydrocarbon streams, and the eliluent mixture of steam andhydrofluoricr acid was separable to yield substantially anhydroushydrouoric acid.

Example III In a system for the continuous hydrofluoric acid alkylationof isobutane with a mixture of butenes, the eliluent from the alkylatoris passed to a settler, in which, by means of gravity the efuent isseparated into two liquid phases. The heavier or acidphase is recycledto the alkylator and the lighter or hydrocarbon phase is passed to anazeotrope column, in which the dissolved hydrogen fluoride is removed asa low-boiling mixture with isobutane. The kettle fraction, which iscomposed of substantially hydrogen fluoride-free hydrocarbons and aminor proportion of organic iiuorine compounds, is passed through adeuorination chamber containing dehydrated bauxite at a temperature ofabout 180 F. and a space velocity of about 2.0 liquid volumes per volumeof catalyst per hour. After a period of such operation, the bauxite hasa fluorine content of approximately 40 weight per cent. Thedefluorination with this bauxite is discontinued by passing thehydrocarbon stream through another chamber, Which contains freshbauxite. Superheated steam at a temperature of 900 F. is passed throughthe usedv bauxite.- The eiiiuent steam is cooled to 240 F. and is passedto an absorber in which the steam at approximately atmospheric pressureis contacted with potassium fluoride on an inert support maintained at240 F. to absorb the hydrouoric acid formed in the regeneration of theused bauxite. Periodically, the potassium uorde absorber is cut 01T fromthe steam regeneration system to recover the hydrofluoric acid byheating the potassium fluoride complex with butane vapor at 600 F. Theellluent vapor stream is condensed by cooling and the lower liquidhydrofiuoric acid layer is recycled to the alkylator, and the upperliquid butane is sent to a heater to be vaporized and heated beforebeing returned to the potassium fluoride complex to remove ad'- ditionalhydrouoric acid. The potassium fluoride absorber is then reusedforvabsorbing more hydrofluoric acid from the regeneration steam. Theregenerated bauxite is suitable for reuse for deuorination.

Example IV In an exploratory experiment, a constantboiling aqueoussolution containing 38 per cent by Weight of hydrofluoric acid wasvaporizedxand passed at y347 F. throughabed'of charcoal-imypregnatedwith 30 per, cent of its own Weight of potassium uoride; the.eluent contained only 0.1 per cent by Weightof hydroiluoric acid. Theadsorbed hydrofluoric acid was partly removed by passage of nitrogenthrough the bed at 617 F., until the eiuent nitrogen contained only 0.35per cent by Weight of hydrofiuoric acid. Then vaporized 38 per centhydrouoric acid was passed through the bed at 257 F.; the eiiluentcontained 0.35v per cent by weight of hydro uoric acid. Hydrofluoricacid adsorbed in this second adsorption was then removed .by passage ofnitrogen through the bed at 527 F. Vaporized 38 per cent hydrofluoricacid was again passed through the bed at 257 F., until the bed wassaturated and the eflluent contained. as much hydroluoric acid as thefeed. The bed gave Voi a large proportion of the adsorbed hydrouoricacid on being heated to 662 F.; passage of nitrogen through the bed atthis temperature desorbed additional hydrofluoric acid, so that thetotal hydrouoric acid recovered amounted to 88 per cent by Weight of thepotassium uoride in the bed.

The invention may be practiced in many Ways other than those specicallydescribed .and many modifications Within the scope of the invention willbe obvious to those skilled in the art, in the light of the presentdisclosure and-discussion, so that the invention should not be undulyrestricted by the foregoing specification and examples.

I claim:

1. A- processrfor the recovery of fluorinev in the form of hydroluoricacid from a hydrocarbon material containing said fluorine in the formvof an organic uorine compound, which comprises deuorinating saidhydrocarbon material byv con tact With a porous metal oxide deuorinatingagent under such defluorination conditionsV that said fluorne is removedfrom said hydrocarbon material and is retained by said` deiiuorinatingagent, subsequently removing the fluorine as hydroiiuoric acid bytreating the defluorinating agent with superheated steam at atemperature above approximately 600 F. to convert retained iuorine tohydrogen fluoride and to elect removal of hydrogen fluoride therefrom,absorbing hydrogen fluoride from the resulting vaporous mixture with aiiuoride of a metal of the group consisting of the alkali and the alkaliearth metals at a temperature not greater than about 400 F. and underconditions of temperature and pressure such thaty a liquid aqueous phaseis not present and the partial pressure of the hydrogen uoride issubstantially greater in said resulting vaporous mixture than is thepartial pressure of hydrogen fluoride in said metal fluoride, andsubsequently desorbing hydrogen uoride from said metal fluoride.

2. A process for the recovery of uorinein the form of hydroiiuoric acidfrom a hydrocarbon material containing said fluorine in the form of4organic fluorine compounds, which comprises defluorinating saidhydrocarbon material by contact with a porous metal oxide deuorinatingagent under such defluorination conditions that said fluorine is removedfrom said hydrocarbon material and is retained by said defluorinatingagent, subsequently removingV theV uorine as hydrouorio acid by treatingthe defluorinating agent with superheated steam at a temperature aboveapproximately 600 F. to convert retained uorine to hydrogen-fluoride andto effectv re-V moval of hydrogen fluoride therefrom, absorbing hydrogenuoride from the resulting vaporous mixture with a fluoride of a metal ofthe group consisting of the alkali and alkali earth metals at atemperature of approximately 240 F. and at a pressure of approximatelyatmospheric, and subsequently desorbing hydrogen fluoride from saidmetal fluoride With a stream of butane at approximately 600 F.

3. A process for the recovery of fluorine in the form of hydrofluoricacid from a hydrocarbon material containing said fluorine in the form oforganic iluorne compounds, which comprises defluorinating saidhydrocarbon material by contact with a porous metal oxide deluorinatingagent under such defluorination conditions that said iiuorine is removedfrom said hydrocarbon material and is retained by said deiluorinatingagent, subsequently removing the iiuorine as hydrofluorie acid bytreating the deuorinating agent With superheated steam at a temperatureabove approximately 600 F. to convert retained fluorine to hydrogenfluoride and to effect removal of hydrogen fluoride therefrom, absorbinghydrogen fluoride from the resulting vaporous mixture with potassiumfluoride at a temperature of approximately 240 F. and at a pressure ofapproximately atmospheric, and subsequently desorbing hydrogen iluoridefrom said potassium fluoride with a stream of butane at approximately600 F.

4. The process for recovering hydrogen fluoride in a concentrated formfrom aqueous hydroiiuoric acid, which comprises absorbing hydrogenuoride Ifrom said aqueous hydrouoric acid With a iluoride of a metal ofthe group consisting of the alkali and the alkali earth metals at atemperature not greater than about 400 F. and under conditions oftemperature and pressure such that a liquid aqueous phase is not presentand the partial pressure of the hydrogen fluoride is substantiallygreater in said resulting vaporous mixture than is the partial pressureof hydrogen iiuoride in said metal fluoride, subsequently passing avaporous low-boiling parailnic hydrocarbon over the resultinguorine-enriched metal fluoride at a sufficiently elevated temperatureand low pressure to desorb hydrogen uoride, cooling and condensing theresulting vaporous hydrocarbon-hydrogen fluoride mixture to form aliquid hydrocarbon-rich phase and a liquid hydrogen fluoride-rich phase,and recovering liquid concentrated hydrogen fluoride.

5. The process of claim 4 in which said lowboiling parainic hydrocarbonis butane.

6. The process for recovering hydrogen fluoride in a concentrated formfrom aqueous hydrouoric acid, which comprises absorbing hydrogen uoridefrom said aqueous hydrouoric acid with a fluoride of a metal of thegroup consisting of the alkali and alkali earth metals at a temperatureof approximately 240 F, and at a pressure of approximately atmospheric,subsequently desorbing hydrogen uoride from said metal fluoride with astream of butane at approximately 600 F., cooling and condensing theresulting vaporous butane-hydrogen iluoride mixture to form a liquidbutane-rich phase and a liquid hydrogen fluoride-rich phase, andrecovering liquid concentrated hydrogen iiuoride.

JAMES D. GIBSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,267,730 Grosse Dec, 30, 19412,333,649 Grosse et al. Nov. 9, 1943 1,869,781 Shiiiler Aug. 2, 19322,300,235 Pines Oct. 27, 1942 2,320,629 Matuszak June 1, 1943 2,322,800Frey June 29, 1943 2,333,649 Grosse Nov. 9, 1943 2,347,945 Frey May 2,1944 2,347,317 Gibson April 25, 19.44 2,341,567 Moriarty Feb, 15, 1944OTHER REFERENCES Ikebe et al., Chemical Abstracts, vol. 26, page 1405(1932). (Copy in Sci. Lib.)

Tananaev, Chemical Abstracts, Vol. 32, page 4867 (1938). (Copy inScientific Library.)

Tech. Sect. Nat. Pet. News, June 2, 1943, vol. 35, No. 22, pages R243,R244, 260683.4.

